| 摘要 |
PURPOSE:To make an actuator unnecessary by providing a means to change the refractive index of a lens of converging a light on an optical memory medi um. CONSTITUTION:When a focus point is located on the optical memory medium 2, a focusing error signal from a focusing error detector 6 is assumed to be 'O'. When the optical memory medium 2 slips off from a focused position, the focusing error signal is led to focusing error operator 11, and fed back to an input signal to a refractive index varying electrode 4, and the focusing error operator 11 operates the signal so that the focusing error signal is can- celled and the focus point is focused on the optical memory medium 2, and as a result, it changes the refractive index of an objective lens 3 and the focus point is focused on the optical memory medium 2. Accordingly, it functions as an automatic focus control device to follow up a focused state, even if the optical memory medium 2 slips off. Because a mechanically movable part like the actuator does not exist, a device can be easily miniaturized. |
